Metallic stenting, especially in cardiovascular angioplasty, has become important in simplifying surgical procedures and reducing patient hospital stays. Most significantly, stenting has dramatically reduced restonosis.
Several issues, however, still remain for metallic based stents. These include thrombogenicity and persistence of restonosis in some patients, poor capabilities to deliver drugs, and damage to the lumen during expansion. Furthermore, in some instances, such as stenting of the urethra after surgical intervention for benign prostate hypertrophy (BPH) to prevent post-operative urinary retention, it would be highly desirable to have a stent formed from a polymer which keeps the lumen open until swelling has subsided, then is passed in the urine stream.
One potential method to overcome these challenges is to provide an absorbable stent which is engineered with the proper strength and stiffness to resist the hydrostatic, axial and compressive loads in a tubular vessel (e.g., urethra), but not over-engineered to cause tissue damage, as in the case of metals, can be expanded to conform to the organ's vessel walls, and can deliver drugs to specific sites, both in the lumen and in the body fluids (e.g., urine, bile). In addition, the device should maintain the advantages of metallic stents such as flexibility for ease in delivery, thinness in its walls so as to not disrupt fluid flow, radio-opaqueness for post-operative management, and support for the organ's vessel wall until healing has occurred.
Several patents describe absorbable stents to overcome the disadvantages of metallic stenting. However, these either require the use of a balloon catheter to expand them, and/or are not sufficiently flexible in any direction transverse to their longitudinal axis. Examples of such stents, along with their use of pores to allow tissue ingrowth, are shown in, e.g., U.S. Pat. Nos. 5,059,211; 5,171,262; 5,551,954; and European Patent Application 183,372.
Yet another approach is to use a resorbable or non-resorbable coil spring stent that is collapsed within or on an insertion device for insertion into, e.g., a urethra, but which when ejected from the insertion device automatically expands. Such a stent does not need the use of a balloon catheter. However, insertion and placement within the urethra occurs while the stent is confined within or on an insertion device. Such a requirement can reduce flexibility transverse to the longitudinal axis, because of that insertion device. As a result, the placement of the stent might not easily accommodate sharp turns in the body lumen in which the stent is being placed. Examples of such stents include those shown in U.S. Pat. Nos. 5,160,341 and 5,246,445.
Therefore, what has been needed prior to this invention is a device which is flexible during delivery and deployment so as to ensure easy pass through long tortuous paths and will expand to match the diameter of the tissue lumen, and additionally, dramatically increases in radial stiffness after deployment to resist hydrostatic and compressive pressures.